For automotive parts, electrical parts and the like, it becomes necessary to seal the inside from the outside in some cases, in order to prevent internal liquid and gas from leaking outward, or to the contrary, in order to prevent external liquid, gas, dirt and the like from entering inward. Usually, tight seal or sealing can be obtained by bringing members into close contact with each other. However, when hard ones are brought into close contact with each other, it is difficult to obtain an effective sealing effect. In that case, a member such as a relatively soft sheet such as a packing or a gasket or an O-ring is put therebetween, and pressure contacting is performed. At this time, a portion to be brought into abutting contact is usually called a flange. This packing or solid gasket is formed by die molding of paper, cork, rubber or the like or stamping of a sheet.
The above-mentioned packing or solid gasket is required for each form of a part to be sealed, so that there are disadvantages of the increased number of parts and the difficulty of automating incorporation into a part to be sealed, although this is a well-known problem. Accordingly, on-site forming gaskets have been abundantly used in which a liquid sealing member is applied to a flange portion of a part to be sealed, and cured. The on-site forming gaskets are roughly classified into three types. The first is a mold in-place gasket (MIPG) method comprising previously bringing a mold into pressure contact with a flange of a part to be sealed, injecting a liquid sealing member such as a heat curable silicone into a cavity formed between the mold and the flange, and curing it to form a gasket, the second is a formed in-place gasket (FIPG) method comprising automatically applying a liquid sealing material such as a room-temperature (moisture) curable or two-component mixing curable silicone to a flange of a part to be sealed, bringing a flange of another part to be sealed into pressure contact therewith, and aging it for a specified time to cure the liquid sealing material between the flanges, and the third is a cured in-place gasket (CIPG) method comprising applying a liquid sealing material such as a two-component mixing curable or room-temperature (moisture) curable silicone in bead form, and aging or heating it as such for a specified time to form a sealed portion.
The MIPG requires the preparation of a mold for each part to be sealed, so that it is not adequate to small-lot large item products. Moreover, a production technique for preventing the occurrence of burrs is also not easy. The FIPG is easily automated, and in curing and aging, the parts can be allowed to stand as they are combined in many cases. Accordingly, it is excellent in productivity. However, the flanges of the parts to be sealed are laminated at the time when curing has not been caused, so that a sealing layer formed or the sealing material between the flanges becomes a thin film. This is as the flanges are adhered to each other, and shows extremely high seal pressure resistance. On the other hand, one used under severe conditions such as high-temperature conditions or violently vibrating conditions has the possibility that the sealing layer is broken or the possibility that separation occurs at an interface between the sealing material and the flange. Accordingly, the use in such a portion has come to be feared. The CIPG comprises forming the sealing material in bead form, and bringing it into pressure contact with the flange of another member to be sealed. Sealing properties have been maintained by repulsive force generated from elasticity of the sealing material. For that reason, in order to exhibit a long-term sealing effect, it has been necessary that repulsive force is maintained for a long time, that is to say, that a sealing material having low compression set is used.
The sealing material used in the above-mentioned on-site forming gasket is practically one containing an organopolysiloxane as a main component. The organopolysiloxane is referred to as a so-called silicone resin, and excellent in heat resistance and handleability. Many prior art documents including patent document 1 and patent document 2 have been published.    Patent Document 1: JP-A-63-251488    Patent Document 2: JP-A-5-246456
However, in recent years, in portions such as an engine portion in which an engine oil, a gear oil or the like must be sealed at high temperatures, portions have increased in which an oil containing an extreme-pressure additive in increased amounts is used in order to improve lubricating performance. When the silicone resin is used in this site, there has come to cause the problem that the extreme-pressure additive contained in the oil breaks the bond of the organopolysiloxane to deteriorate the sealing material. In particular, in the CIPG, the seal form is in bead form, so that the area which contacts with the oil is large, and the possibility of being deteriorated is high. Accordingly, as described in patent document 3, there is proposed a sealing material using a so-called acrylic rubber in which an acrylic ester is copolymerized, without using the silicone resin. The acrylic rubber is little deteriorated by the extreme-pressure additive, compared to the silicone resin, and useful to such a portion. However, the acrylic rubber represented by patent document 3 is solid at ordinary temperature, so that it can only be used as a solid packing, and has not been able to be readily used in a technique of applying a liquid material and curing it, such as the FIPG or the CIPG.    Patent Document 3: JP-A-8-284746
On the other hand, from long ago, there has been proposed a technique of adding a reactive functional group into a molecule of a relatively low molecular weight copolymer of an acrylic ester and reacting the reactive functional group, thereby performing curing. That is described in patent document 4 and the like. When a composition described in patent document 4 is used, it can be easily applied, because it is liquid at the time of coating, and when it is cured, oil resistance of the acrylic rubber is exhibited. It is therefore an extremely useful composition. However, it is practically difficult to selectively add the reactive functional group in a copolymerization reaction of the acrylic ester, and such a resin has not commercially come in practice. In recent years, reactive liquid acrylic rubbers have been developed by methods described in patent documents 5 to 8 and the like, resulting in the possibility of practical use.    Patent Document 4: JP-A-61-133201    Patent Document 5: JP-A-11-80250    Patent Document 6: JP-A-2000-38404    Patent Document 7: JP-A-2001-271055    Patent Document 8: JP-A-2002-69121